FIGS. 1A-D illustrate the problem of presbyopia. FIGS. 1A-B illustrate that a non-presbyopic eye 1 can image both a distant object and a nearby object to the retina 3 by changing the shape of a crystalline lens 5. FIGS. 1C-D illustrate that a presbyopic eye 1 loses its ability to image nearby objects to the retina 3, because the flexibility of the crystalline lens 5 is diminished by the advancing age of the patients. When looking at a nearby object, the crystalline lens 5 cannot accommodate and change its shape to a sufficient degree, and the object gets imaged behind the retina.
Presbyopia is often alleviated by prescribing bifocal, multifocal, and progressive lenses that focus some light at a primary focus and then distribute the remaining light to one or more other foci. These lens designs can be employed in eye glasses, in contact lenses, and in intraocular lenses (IOLs), inserted into the eye 1 during cataract surgery.
Some other approaches improve the visual acuity of presbyopic eyes by extending the depth of focus of the eye by reducing its aperture. Such aperture-reducing designs can deliver notable improvements. There are already products that utilize this design, such as the aperture-decreasing corneal inlays from AcuFocus. These are essentially small, non-transparent discs, with apertures in its middle that act as artificial pupils.
However, such “hard” aperture devices have drawbacks, such as reduced luminescence, and sensitivity to the quality of centration, since an off-center aperture can undermine and degrade visual acuity.
Other systems address presbyopia differently. An analysis of the wave nature of light reveals that the blue spectral component of an image formed by a presbyopic eye on the retina is the blurriest, and the red spectral component of its image is the least blurry. Some IOL manufacturers therefore add a blue filter to their IOLs. Such filters can reduce the blurriest blue component of an image.
However, such blue-filtering IOLs have their own problems, including changes in the color perception of the patient. Therefore, there is still an unmet medical need for new approaches that improve the visual acuity of presbyopic eyes.